TLS-N: Non-repudiation over TLS Enabling Ubiquitous ... · TLS-N: Non-repudiation over TLS Enabling Ubiquitous Content Signing Hubert Ritzdorf, Karl Wüst, Arthur Gervais, Guillaume

TLS-N: Non-repudiation over TLSEnabling Ubiquitous Content SigningHubert Ritzdorf, Karl Wüst, Arthur Gervais, Guillaume Felley, Srdjan Capkun

ETH Zurich

Karl Wüst 2018-01-26 1

TLS

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{ ↔ �}µ

Karl Wüst 2018-01-26 2

TLS

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µ

{ ↔ �}µ

Karl Wüst 2018-01-26 2

TLS

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µ

{ ↔ �}µ

Karl Wüst 2018-01-26 2

TLS

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µ

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Karl Wüst 2018-01-26 2

Web Archive

Karl Wüst 2018-01-26 3

Blockchain Oracles

® Y �Blockchain Oracle World

pp

Karl Wüst 2018-01-26 4

Blockchain Oracles


pp

Karl Wüst 2018-01-26 4

Blockchain Oracles


pp

Karl Wüst 2018-01-26 4

Blockchain Oracles


pp

Karl Wüst 2018-01-26 4

Non-Repudiation for TLS

Verifier(third party/blockchain)

Generator(server)

Requester(client)

CA

TLS Conversation

Provides Evidence

Sends ProofTrusts

Create Proof fromEvidence and Plaintext

VerifiesIdentity

Karl Wüst 2018-01-26 5



Generator(server)

Requester(client)

CA

TLS Conversation

Provides Evidence

Sends ProofTrusts

Wants to learn about


VerifiesIdentity

Karl Wüst 2018-01-26 5



Generator(server)

Requester(client)

CA

TLS Conversation

Provides Evidence

Sends ProofTrusts



VerifiesIdentity

Karl Wüst 2018-01-26 5



Generator(server)

Requester(client)

CA

TLS Conversation

Provides Evidence

Sends ProofTrusts



VerifiesIdentity

Karl Wüst 2018-01-26 5



Generator(server)

Requester(client)

CA

TLS Conversation

Provides Evidence

Sends ProofTrusts

Learns about


VerifiesIdentity

Karl Wüst 2018-01-26 5

Possible Problems - Content Reordering

Client Server

Req xCollect Evidence

123

Req yReturn Evidence

Evidence(Req y+123)

987

Evi

denc

eW

indo

w

Client Server

Req y

123

Karl Wüst 2018-01-26 6


Client Server


123


Evidence(Req y+123)

987

Evi

denc

eW

indo

w

Client Server

Req y

123

Karl Wüst 2018-01-26 6


Client Server


123


Evidence(Req y+123)

987

Evi

denc

eW

indo

w

Client Server

Req y

123

Karl Wüst 2018-01-26 6


Client Server


123


Evidence(Req y+123)

987

Evi

denc

eW

indo

w

Client Server

Req y

123

Karl Wüst 2018-01-26 6

Possible Problems - Privacy

GET /me?fields=id&access_token=EAACEdEose0cB... HTTP/1.1

Host: graph.facebook.com

→ Need redactable proofs!

Karl Wüst 2018-01-26 7





Karl Wüst 2018-01-26 7





Karl Wüst 2018-01-26 7

Possible Problems - Denial of Service

• 1 signature over everything→ possibly large state

• Server side redacting→ computational overhead

Karl Wüst 2018-01-26 8


• 1 signature over everything

→ possibly large state


Karl Wüst 2018-01-26 8




Karl Wüst 2018-01-26 8



• Server side redacting

→ computational overhead

Karl Wüst 2018-01-26 8




Karl Wüst 2018-01-26 8

Goals

• Small server side state & overhead

• Client side privacy protection

• Clear context → total order on records

Karl Wüst 2018-01-26 9

Goals




Karl Wüst 2018-01-26 9

Goals




Karl Wüst 2018-01-26 9

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence

Save TLS Recordsand TLS-N

parameters fromthe handshake

ProofGeneration

User’s PrivacySettings

2

Evidence Generation:Steady Processing

of TLS Recordswith small state

Sign TLS Private Key

Karl Wüst 2018-01-26 10

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence



ProofGeneration


2




Karl Wüst 2018-01-26 10

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence



ProofGeneration


2




Karl Wüst 2018-01-26 10

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence



ProofGeneration


2




Karl Wüst 2018-01-26 10

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence



ProofGeneration


2




Karl Wüst 2018-01-26 10

TLS-N Overview

Client Server

TLS Handshake

Req x

123

Req y

987

Return Evidence

Evidence



ProofGeneration


2




Karl Wüst 2018-01-26 10

Record Level Privacy Protection

Record 0

C

c0,0

Salt Secret0

ENonce

TLS Traffic Secret HO0

0x0lR0

H0x1

h0

Record 1

C

c1,0

Salt Secret1

HO1

0x0lR1

H0x1

h1

Record 2

C

c2,0

Salt Secret2

HO2

0x0lR2

H0x1

h2

hc0 hc1 hcn−1

Ordered TLS Conversation Records

Hash Chain

Karl Wüst 2018-01-26 11


Record 0

C

c0,0

Salt Secret0

ENonce


0x0lR0

H0x1

h0

Record 1

C

c1,0

Salt Secret1

HO1

0x0lR1

H0x1

h1

Record 2

C

c2,0

Salt Secret2

HO2

0x0lR2

H0x1

h2

hc0 hc1 hcn−1


Hash Chain

Karl Wüst 2018-01-26 11


Record 0

C

c0,0

Salt Secret0

ENonce


0x0lR0

H0x1

h0

Record 1

C

c1,0

Salt Secret1

HO1

0x0lR1

H0x1

h1

Record 2

C

c2,0

Salt Secret2

HO2

0x0lR2

H0x1

h2

hc0 hc1 hcn−1


Hash Chain

Karl Wüst 2018-01-26 11

Chunk Level Privacy Protection

S0,0 S0,1 S0,2 S0,3 S0,4 S0,5 S0,6 S0,7

E

S10,0

E

S10,1

E

S10,2

E

S10,3

E

S20,0

E

S20,1

E

Salt Secret0

ENonce

TLS Traffic Secret

Salt Tree

Record 0Record 0

C

c0,0

C

c0,1

C

c0,2

C

c0,3

C

c0,4

C

c0,5

C

c0,6

C

c0,7

H

h10,0

H

h10,1

H

h10,2

H

h10,3

H

h20,0

H

h20,1

HO0 lR0

0x0

Record 1Record 1

S21,0 S2

1,1 S21,2 S2

1,3

C

c1,0

C

c1,1

C

c1,2

C

c1,3

H

h11,0

H

h11,1

HO1

0x0lR1

Record 2Record 2

S22,0 S2

2,1 S22,2 S2

2,3

C

c2,0

C

c2,1

C

c2,2

C

c2,3

H

h12,0

H

h12,1

HO2

0x0lR2

H0x1h0

H0x1

h1

H0x1

h2

hc1hc0 hcn−1


Hash Chain

Karl Wüst 2018-01-26 12


S0,0 S0,1 S0,2 S0,3 S0,4 S0,5 S0,6 S0,7

E

S10,0

E

S10,1

E

S10,2

E

S10,3

E

S20,0

E

S20,1

E

Salt Secret0

ENonce

TLS Traffic Secret

Salt Tree

Record 0Record 0

C

c0,0

C

c0,1

C

c0,2

C

c0,3

C

c0,4

C

c0,5

C

c0,6

C

c0,7

H

h10,0

H

h10,1

H

h10,2

H

h10,3

H

h20,0

H

h20,1

HO0 lR0

0x0

Record 1Record 1

S21,0 S2

1,1 S21,2 S2

1,3

C

c1,0

C

c1,1

C

c1,2

C

c1,3

H

h11,0

H

h11,1

HO1

0x0lR1

Record 2Record 2

S22,0 S2

2,1 S22,2 S2

2,3

C

c2,0

C

c2,1

C

c2,2

C

c2,3

H

h12,0

H

h12,1

HO2

0x0lR2

H0x1h0

H0x1

h1

H0x1

h2

hc1hc0 hcn−1


Hash Chain

Karl Wüst 2018-01-26 12


S0,0 S0,1 S0,2 S0,3 S0,4 S0,5 S0,6 S0,7

E

S10,0

E

S10,1

E

S10,2

E

S10,3

E

S20,0

E

S20,1

E

Salt Secret0

ENonce

TLS Traffic Secret

Salt Tree

Record 0Record 0

C

c0,0

C

c0,1

C

c0,2

C

c0,3

C

c0,4

C

c0,5

C

c0,6

C

c0,7

H

h10,0

H

h10,1

H

h10,2

H

h10,3

H

h20,0

H

h20,1

HO0 lR0

0x0

Record 1Record 1

S21,0 S2

1,1 S21,2 S2

1,3

C

c1,0

C

c1,1

C

c1,2

C

c1,3

H

h11,0

H

h11,1

HO1

0x0lR1

Record 2Record 2

S22,0 S2

2,1 S22,2 S2

2,3

C

c2,0

C

c2,1

C

c2,2

C

c2,3

H

h12,0

H

h12,1

HO2

0x0lR2

H0x1h0

H0x1

h1

H0x1

h2

hc1hc0 hcn−1


Hash Chain

Karl Wüst 2018-01-26 12

Properties

• Non-repudiation

• Privacy Preserving

• Redactions are visible to verifiers

• Order preserving

• Efficient

Karl Wüst 2018-01-26 13

Properties

• Non-repudiation




• Efficient

Karl Wüst 2018-01-26 13

Properties

• Non-repudiation




• Efficient

Karl Wüst 2018-01-26 13

Properties

• Non-repudiation




• Efficient

Karl Wüst 2018-01-26 13

Properties

• Non-repudiation




• Efficient

Karl Wüst 2018-01-26 13

Properties

• Non-repudiation




• Efficient

Karl Wüst 2018-01-26 13

Flight Insurance (1)

InsuranceProvider

Flight InsuranceContract

Airline WebsiteCustomer

Claim

Ok (or Timeout)

Payo

ut

Karl Wüst 2018-01-26 14


InsuranceProvider



Claim

Ok (or Timeout)

Payo

ut

Karl Wüst 2018-01-26 14


InsuranceProvider



Claim

Ok (or Timeout)

Payo

ut

Karl Wüst 2018-01-26 14


InsuranceProvider



Claim

Ok (or Timeout)

Payo

ut

Karl Wüst 2018-01-26 14


InsuranceProvider



Claim

No!

TLS Sessionwith TLS-N

Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15


InsuranceProvider



Claim

No!


Proof

VerifiesContents

Payo

ut

Karl Wüst 2018-01-26 15

Smart Contract Costs

Conversation Size1 KB 10 KB

secp256r1 secp256k1 secp256r1 secp256k1

Cos

ts(2

018-

01-2

3)

Basic Gas 119,758 737,159Total Gas 1,284,723 131,286 1,938,872 782,219Ether 0.0434 0.0044 0.0655 0.0264USD 41.08 4.20 62.00 25.01

Karl Wüst 2018-01-26 16

Related Work

Town Crier

• SGX based blockchain oracle

• Allows offline computation

• Does not require server modifications

• Requires additional trust assumptions

Karl Wüst 2018-01-26 17

Related Work

TLS-Notary

• Not compatible with TLS 1.2 & 1.3

• Additional TTP required for non-interactive use

• Used by Oraclize

Karl Wüst 2018-01-26 18

Related Work

Other Proposals for TLS Extensions

• TLS Evidence (incomplete IETF draft)

→ Reordering Attack

• TLS Sign (incomplete IETF draft)

→ Reordering Attack

• MAC Chaining (IETF mailing list)

→ Forgery Attack

Karl Wüst 2018-01-26 19

Related Work

Other Proposals for TLS Extensions

• TLS Evidence (incomplete IETF draft)→ Reordering Attack

• TLS Sign (incomplete IETF draft)→ Reordering Attack

• MAC Chaining (IETF mailing list)→ Forgery Attack

Karl Wüst 2018-01-26 19

Try it out: https://tls-n.org

• Research Paper

• Interactive Proof Generation

• Code for the TLS extension (NSS library)

• Smart Contract Library

• Example Smart Contract

Karl Wüst 2018-01-26 20

https://tls-n.org

Karl Wüst 2018-01-26 21

Figure: Proof generation and proof verification times for random, simulatedTLS sessions (client side).

0 2 4 6 8 10Conversation Size of Session (MB)

0

1000

2000

3000

4000

5000Tim

e(m

s)Proof Generation: Chunk-level (16 B)

Proof Verification: Chunk-level (16 B)

Proof Generation: Record-level

Proof Verification: Record-level

Karl Wüst 2018-01-26 22

Overhead - Processing Time

0 2 4 6 8 10 12 14 16Record Length (KB)

0

2

4

6

8

10

12

14

16Tim

e(m

s)

Chunk-level (8 B)

Chunk-level (16 B)

Chunk-level (32 B)

Chunk-level (64 B)

Record-level

Karl Wüst 2018-01-26 23

Overhead - Requesting a File

10 B 100 B 1 KB 10 KB 100 KB 1 MB 10 MBSize of Requested File

100

101

102

103

Tim

e(m

s)

TLS-N Enabled

TLS-N Disabled

Overhead

Karl Wüst 2018-01-26 24

Documents

TLS-N: Non-repudiation over TLS Enabling Ubiquitous ... · TLS-N: Non-repudiation over TLS Enabling Ubiquitous Content Signing Hubert Ritzdorf, Karl Wüst, Arthur Gervais, Guillaume